Dell Studio 1555: Power Problem

Hi,

Whenever i press the power button it is mainly unresponsive. I have to hold the button for about 3 seconds until it powers up. It sometimes cuts out either a few seconds in, or maybe 1-2 mins. I've only had this problem for a few hours so its not completly tested as of yet. I've only just managed to get it working, but im afraid of knocking it, as sometimes it dies from a knock. Nothing extra was connected to the laptop. It has a full battery, and charger in. I've tried taking the power out and just using battery, reinserting the battery and still plays up.

What can be causing this? Is it a loose connection somewhere or has something gone/going? The laptop is out of warranty, and I don't want to take it to a shop. Im not too fussed with doing a few minor tasks to it (im not too bad with PCs).

A few mates friends have told me it could be overheating or maybe a loose connection. Unsure it's overheating as it can turn off after a few seconds, which i doubt it can get too hot within that time.